Effect Of Molecular Structures Of Waterborne Polyurethane On The Adhesive Properties

The waterborne polyurethane (WPU) adhesive is a binary colloidal system which isformed by using polyurethane to dissolve in water or disperse in water. Compared with thesolvent-based polyurethane, WPU has many outstanding advantages，such as innocuity,having resistance for burning, and not contamination environment, etc., but there are alsosome disadvantages of the low bonding properties. In order to effectively improve thebonding strength, the relationship between of molecular structure and bonding strength hasbeen researched in this paper, which is of great significance for the WPU to expand the rangeof applications.Bonding strength of WPU is be influenced by the molecular structure. The changes in themolecular structure is mainly reflected three aspects: the type、location and content of thepolar group in the molecular chain. In this thesis, isophorone diisocyanate (IPDI) has been ashard segment, polytetramethylene glycol (PTMG) and polycaprolactone glycol (PCL) is softsegment, dimethylol propionic acid (DMPA) is hydrophilicthe chain extender,1,4-butanediol(BDO)、ethylene diamine (EDA) and3,3`-dichloro-4.4`-diphenylmethane diamine (MOCA) ischain extender, the prepolymer dispersion method has been adopted, the R value (the ratioof NCO/OH)、the hard segment、the soft segment and chain extender of different molecularstructural WPU on the bonding strength is be studied. The mechanical properties and bondingstrength of film samples were analyzed by electronic tensile machine, and the analysis resultshowed: with increasing the R value,the the tensile shear strength、tensile strength and peelstrength can be improved. However, if the R value was too high, the increase of adhesionproperties of WPU is difficult. The tensile shear strength、peel strength and tensile strength ofPCL-WPU is higher than that of PTMG-WPU. The increasing of the polyether soft segmentwould lead to decrease of bonding strength and tensile strength of WPU. It was moresignificant to improve the adhesive performance by using amine chain extender than those byusing alcohols chain extender.In addition, the anionic water borne polyurethane was modified by using the silicone. Amino groups of silicone created crosslinking with polyurethane prepolymer, thereby therewere higher polar urea bonds and a three-dimensional net-like structure in molecular structureof WPU. The test results of the mechanical properties and bonding strength showed that thetensile shear strength、tensile strength and peel strength of modified WPU were increased insome extent. The heat resistance of samples were analyzed by using thermal gravimetricanalysis (TGA), and the result found that initial decomposition temperature of modified WPUincrease. Compared with the unmodified WPU, the modified WPU had higher thermalstability and heat resistance, and showed excellent comprehensive performance.